Modern cardiac surgical management of congenital heart defects allows corrective and palliative techniques to be applied successfully to the newborn. However, many with severe cardiac malformations are left with lifelong cardiovascular disability and risk due to the cumulative damage caused by these cardiac lesions on myocardial structure and function that occur during fetal life. Recently, percutaneous and transuterine interventional have been developed to treat severe congenital cardiac defects in the 2nd and early 3rd trimester of pregnancy, before the natural history of these lesions results in permanent developmental injury to the heart. The challenges currently facing practitioners of these novel interventional approaches are technical in nature, and include difficulties in interpretation of planar ultrasonographic imaging, navigation of interventional instruments, positioning and immobilization of the fetus, design and use of tools that are optimized to the dimensions and material properties of fetal tissue, and the precision and speed with which access to the fetal heart can be obtained. Identification of these challenges has prompted us to develop algorithms for image-guided techniques using real time 3D ultrasound and electromagnetically guided instrument navigation as a multimodal platform to guide performance of fetal cardiac interventions. Preliminary investigation by this group has shown that the complex but generalizable problem of locating a hidden fetal anatomical target for precise percutaneous intervention may be greatly facilitated using this approach. The overall goal of this proposal is to enable controlled and reproducible fetal cardiac intervention by integration of real time 3D ultrasound imaging, electromagnetic navigation of instruments and development of devices for reduction of fetal motion. To achieve this goal, a series of development projects and experiments is proposed to address the following specific aims: 1) optimize real time 3D ultrasound and acoustic properties of therapeutic devices for use in fetal interventional procedures, 2) integrate electromagnetic navigation with 3D ultrasound to enable precise treatment planning and coordinated spatial tracking of imaging and access tools, and 3) develop fixation instruments and needle insertion techniques based the material properties of fetal and maternal tissue. Successful completion of these aims will improve precision, reproducibility, safety and speed of task performance in fetal cardiac interventions. The PI has assembled a team of clinicians and engineers, based both in university and industrial environments, to work collaboratively on in vitro and in vivo studies to develop a robust procedural algorithm and platform for further clinical development of these and other fetal interventions.